In Step-by-Step, type "installment sales" (without the quotes) in the Search box, then click the link that says "Jump to installment sales." Note that you have to use the plural sales, not sale. On the first screen, check the box for installment sales. It will then take you through the interview for an installment sale.
There is no way to search the forms in forms mode. If you need to search for text in the forms, create a PDF and use Ctrl-F in Acrobat Reader to search for the text. But if the help topic that you are talking about is How do I report an installment sale in TurboTax?, it's not telling you to search for text in the forms. It says to open "your return," not your 1040 form. That just means working on your return in Step-by-Step, as you normally would. Step 2 tells you to do what I said above, but you have to use the exact search term that it shows, with plural sales.
